Natural adsorbents as low-cost materials have been proved efficient for water remediation and have significant capacity for the removal of certain chemicals from wastewater. The present investigation aimed to use Citrullus colocynthis seeds (CCSs) and peels (CCPs) as an efficient natural adsorbent for methylene blue (MB) dye in an aqueous solution. The examined biosorbents were characterized using surface area analyzer (BET), scanning electron microscope (SEM), thermogravimetric analyzer (TGA) and Fourier transform infra-red (FT-IR) spectroscopy. Batch adsorption experiments were conducted to optimize the main factors influencing the biosorption process. The equilibrium data for the adsorption of MB by CCSs were best described by the Langmuir isotherm followed by the Freundlich adsorption isotherms, while the equilibrium data for MB adsorption by CCPs were well fitted by the Langmuir isotherm followed by the Temkin isotherm. Under optimum conditions, the maximum biosorption capacity and removal efficiency were 18.832 mg g⁻¹ and 98.00% for MB-CCSs and 4.480 mg g⁻¹ and 91.43% for MB-CCPs. Kinetic studies revealed that MB adsorption onto CCSs obeys pseudo-first order kinetic model (K₁ = 0.0274 min⁻¹), while MB adsorption onto CCPs follows the pseudo-second order kinetic model (K₂ = 0.0177 g mg⁻¹ min⁻¹). Thermodynamic studies revealed that the MB biosorption by CCSs was endothermic and a spontaneous process in nature associated with a rise in randomness, but the MB adsorption by CCPs was exothermic and a spontaneous process only at room temperature with a decline in disorder. Based on the obtained results, CCSs and CCPSs can be utilized as efficient, natural biosorbents, and CCSs is promising since it showed the highest removal percentage and adsorption capacity of MB dye.

中文翻译：

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柑橘种子和果皮作为亚甲基蓝染料的高效天然吸附剂的研究

天然吸附剂作为低成本材料已被证明可有效修复水，并具有显着去除废水中某些化学物质的能力。本研究旨在利用Citrullus colocynthis种子（CCSs）和果皮（CCPs）作为水溶液中亚甲蓝（MB）染料的有效天然吸附剂。使用表面积分析仪 (BET)、扫描电子显微镜 (SEM)、热重分析仪 (TGA) 和傅里叶变换红外 (FT-IR) 光谱对所检测的生物吸附剂进行表征。进行批量吸附实验以优化影响生物吸附过程的主要因素。CCS 吸附 MB 的平衡数据最好由 Langmuir 等温线和 Freundlich 吸附等温线描述，而 CCP 吸附 MB 的平衡数据很好地拟合为 Langmuir 等温线和 Temkin 等温线。在最佳条件下，最大生物吸附容量和去除效率为18.832 mg g ^-1MB-CCS 为 98.00%，MB-CCP 为 4.480 mg g ^-1和 91.43%。动力学研究表明，MB 在 CCS 上的吸附遵循伪一级动力学模型（K ₁ = 0.0274 min ^-1），而 MB 在 CCP 上的吸附遵循伪二级动力学模型（K ₂ = 0.0177 g mg ^-1 min ^-1）。热力学研究表明，CCS 对 MB 的生物吸附是吸热的，并且是自然界中与随机性增加相关的自发过程，但 CCP 对 MB 的吸附是放热的，并且仅在室温下是无序下降的自发过程。根据获得的结果，CCSs 和 CCPSs 可用作高效的天然生物吸附剂，CCSs 具有最高的 MB 染料去除率和吸附能力，因此很有前景。